Method for obtaining hydrogen chloride with low light component content in isocyanate production process

Abstract

The invention belongs to the technical field of phosgene preparation and isocyanate preparation, and particularly relates to a method for obtaining hydrogen chloride with low light component content in an isocyanate production process, which comprises the following steps: (1) synthesizing phosgene from chlorine gas flow and carbon monoxide flow under the catalysis of a catalyst; the inlet temperature of a catalyst bed layer of the phosgene synthesis reactor is controlled to be 110 DEG C or above, and the highest temperature is 450 DEG C or below; (2) condensing and separating the obtained gas-phase material flow I to obtain a liquid phosgene material flow with low content of a light component i; and (3) feeding the liquid phosgene material flow into an isocyanate synthesis process for reaction, and performing condensation and impurity removal on a generated gas phase material flow II to obtain a hydrogen chloride material flow with low content of a light component ii. According to the method, the content of light component impurities in the hydrogen chloride byproduct material can be controlled in a relatively low range, so that the temperature of a catalyst of a hydrogen chloride catalytic oxidation reactor taking hydrogen chloride as a raw material is kept stable, and the stability of an isocyanate production process is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of phosgene preparation and isocyanate preparation, and in particular relates to a method for producing hydrogen chloride (byproduct) with low light component content in the isocyanate production process. Background Art

[0002] In the production process of isocyanate, carbon monoxide and chlorine are usually used as raw materials to prepare phosgene, and then the obtained phosgene is reacted with amines to form isocyanate. The reaction of phosgene and amines to form isocyanate is called phosgenation, and the reaction process will produce a large amount of hydrogen chloride as a by-product.

[0003] For by-product hydrogen chloride, the conventional treatment method is to absorb the by-product hydrogen chloride with water to prepare hydrochloric acid for sale. In order to improve the recycling rate of chlorine elements, chlorine is prepared by the catalytic oxidation process of hydrogen chloride and used as a supporting process in the isocyanate production process. It can be used to treat the by-product hydrogen chloride in the isocyanate production process to produce chlorine and provide raw material chlorine for the production of isocyanates. For example, patent document CN101142173A discloses a method for manufacturing polyisocyanates, which can effectively utilize the hydrogen chloride produced as a by-product in the polyisocyanate manufacturing process, while reducing the load on the environment, and provides a polyisocyanate manufacturing device for implementing the method for manufacturing polyisocyanates; the patent describes in detail the manufacture of isocyanates and the process of preparing chlorine by oxidizing the by-product hydrogen chloride after refining. However, no attention is paid to the temperature stability control of the hydrogen chloride catalytic oxidation reactor when hydrogen chloride is used as a raw material to produce chlorine.

[0004] When using hydrogen chloride produced as a by-product in the isocyanate production process as a raw material to produce chlorine, it is very important to control the temperature stability of the hydrogen chloride catalytic oxidation reactor, because excessively high or unstable catalytic oxidation reaction temperature will lead to a decrease in the life of the catalytic oxidation catalyst or fluctuations in the yield of the chlorine product, thereby affecting the stability of the corresponding isocyanate manufacturing process.

[0005] In conventional processes, carbon monoxide and phosgene are separated by liquefying the synthesized phosgene, and hydrogen chloride with a low carbon monoxide content can be produced as a by-product in the isocyanate production process. For example, patent document CN10448739A discloses a method for separating carbon monoxide from a hydrogen chloride-containing gas, which discloses that carbon monoxide in the hydrogen chloride gas can cause the hydrogen chloride catalytic oxidation catalyst to generate heat and deactivate, and provides a method for reducing the carbon monoxide content in the hydrogen chloride gas stream, thereby producing hydrogen chloride with a low carbon monoxide content as a by-product.

[0006] However, in actual operation, even when the carbon monoxide content in the by-product hydrogen chloride obtained in the isocyanate production process remains stable, it is still observed that the catalyst bed temperature of the hydrogen chloride catalytic oxidation reactor fluctuates or even overheats, passively leading to the shutdown of the hydrogen chloride catalytic oxidation reactor, and the isocyanate production load and process stability are adversely affected.

[0007] Therefore, if the catalyst temperature of the hydrogen chloride catalytic oxidation reactor can be further reduced or stably controlled, it will be very meaningful for the production of isocyanate and is also a direction worthy of research. Summary of the invention

[0008] The object of the present invention is to provide a method for obtaining (by-product) hydrogen chloride with a low light component content in an isocyanate production process in order to solve the technical problems of temperature stability control of a hydrogen chloride catalytic oxidation reactor and stability of isocyanate production. The method can further reduce and maintain the catalyst temperature of the hydrogen chloride catalytic oxidation reactor stable when the by-product hydrogen chloride is used as a raw material for a downstream hydrogen chloride catalytic oxidation device, thereby avoiding abnormal shutdown due to catalyst overheating or temperature fluctuation, and improving the stability of the isocyanate production process.

[0009] A large amount of hydrogen chloride byproduct is produced during the production of isocyanates, which inevitably contains a certain amount of impurities, such as carbon monoxide contained in phosgene, which is the raw material for isocyanate production, carbon dioxide produced during the self-polymerization of isocyanate, and nitrogen introduced during the operation of the device. The hydrogen chloride byproduct is very suitable as a raw material for the downstream hydrogen chloride catalytic oxidation device, because the chlorine gas generated by the catalytic oxidation of the hydrogen chloride byproduct can be used as a raw material for the production of phosgene, realizing the circulation of chlorine resources.

[0010] The inventors of the present application have found that in a hydrogen chloride catalytic oxidation reactor, in addition to the heat released by the catalytic oxidation reaction itself, the light component impurity content in the hydrogen chloride as a raw material has a great influence on the temperature of the catalyst in the hydrogen chloride catalytic oxidation reactor. This is because these light component impurities react with oxygen in the hydrogen chloride catalytic oxidation reactor and also generate a large amount of heat, which leads to fluctuations in the catalyst bed temperature or even over-temperature, and then leads to abnormal shutdown and a decrease in the life of the hydrogen chloride catalytic oxidation catalyst, which has an adverse effect on economic efficiency. Therefore, how to control the light component impurity content in hydrogen chloride as a raw material for the hydrogen chloride catalytic oxidation reaction is crucial to the catalyst bed temperature and stability in the hydrogen chloride catalytic oxidation reaction.

[0011] The inventors of the present application have further studied and found that the light component impurities in the byproduct hydrogen chloride from the isocyanate production process mainly come from the raw material phosgene of the isocyanate production process. It is well known in the art that phosgene is continuously produced using carbon monoxide and chlorine in a shell and tube reactor using activated carbon as a catalyst. In the process of synthesizing phosgene in a shell and tube reactor, under high temperature conditions, chlorine and the catalyst (activated carbon) will react with each other and produce light component substances, such as chlorinated alkanes, chlorinated olefins, etc.; at the same time, excessive carbon monoxide is usually added during the reaction process to ensure that the chlorine is completely converted, and the synthesized phosgene crude product stream also contains a certain amount of carbon monoxide. In the prior art, the synthesized phosgene crude product leaving the phosgene synthesizer is usually separated and treated by condensing the synthesized phosgene crude product to obtain a relatively pure liquid phosgene. However, the liquid phosgene obtained by this method still inevitably contains a certain amount of light components, which will enter the subsequent reaction system with the liquid phosgene, and form non-condensable gas and be discharged from the reactor with the by-product hydrogen chloride, becoming an impurity component in the by-product hydrogen chloride. The inventors of the present application have found through research that by reducing the content of light component impurities in the liquid phosgene flow and controlling the content of light component impurities within a certain range, the light component content in the by-product hydrogen chloride obtained in the isocyanate production process can be reduced, and the catalyst bed temperature can be reduced and the stability can be controlled in the hydrogen chloride catalytic oxidation reaction.

[0012] In order to achieve the above object, the present invention provides the following technical solutions:

[0013] A method for obtaining hydrogen chloride with low light component content in an isocyanate production process comprises the following steps:

[0014] (1) A chlorine gas stream and a carbon monoxide stream are introduced into a phosgene synthesis reactor to carry out a phosgene synthesis reaction under the catalysis of a catalyst to synthesize phosgene; wherein the inlet temperature (or the lowest temperature) of the catalyst bed of the phosgene synthesis reactor is controlled at 110° C. or above, and the highest temperature of the catalyst bed is controlled at 450° C. or below;

[0015] (2) condensing and separating the gas phase stream I discharged from the phosgene synthesis reactor to obtain a liquid phosgene stream with a low content of light component i;

[0016] (3) The obtained liquid phosgene stream is fed into the isocyanate synthesis step as a reaction raw material to carry out a phosgenation synthesis reaction. The gas phase stream II produced by the reaction is condensed and impurities are removed to obtain a hydrogen chloride stream with a low light component II content.

[0017] After the gas phase flow at the outlet of the phosgene synthesis device is separated by condensation, a part of the light component impurities can be removed to obtain liquid phosgene with a low light component content.

[0018] According to the method provided by the present invention, in some embodiments, the liquid phosgene stream contains a light component i, and the composition of the light component includes: one or more of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0019] In some embodiments, in the liquid phosgene stream, the total content (mass ratio) of the light component i is controlled at 5-2000 ppm (e.g., 6 ppm, 10 ppm, 15 ppm, 30 ppm, 50 ppm, 100 ppm, 200 ppm, 400 ppm, 500 ppm, 600 ppm, 800 ppm, 850 ppm, 900 ppm), preferably at 10-1000 ppm, and more preferably at 20-300 ppm.

[0020] The gas phase logistics generated in the isocyanate production process can be processed through a condensation or absorption process to remove the phosgene and solvent components contained in the gas phase logistics to obtain a hydrogen chloride byproduct logistics containing a smaller amount of light components.

[0021] According to the method provided by the present invention, in some embodiments, in the hydrogen chloride stream, the composition of the light component ii includes: one or more of chlorinated olefins, chlorinated alkanes and carbon monoxide;

[0022] In some embodiments, in the hydrogen chloride logistics, the total content (mass ratio) of the light component ii is controlled at 5-1500ppm (for example, 6ppm, 10ppm, 15ppm, 30ppm, 50ppm, 100ppm, 200ppm, 400ppm, 500ppm, 600ppm, 800ppm, 850ppm, 1000ppm, 1200ppm), preferably at 10-750ppm, and more preferably at 20-250ppm.

[0023] In some embodiments, the composition of the light component i and the light component ii is the same or different, preferably the same.

[0024] The phosgene synthesis process usually releases a large amount of heat. If this heat is not removed, it will cause the reaction to overheat and the resulting phosgene product to undergo reverse reaction decomposition. It may also lead to consequences such as catalyst deactivation and equipment damage in the phosgene synthesis process. Therefore, the phosgene synthesis process is usually carried out in a shell-and-tube reactor, and a cooling medium is filled on the side of the reactor shell to remove the heat generated by the reaction to ensure the reaction conversion rate and the safety of the reaction process.

[0025] According to the research of the inventors of the present application on the phosgene synthesis process using activated carbon as a catalyst, it was found that in the phosgene synthesis process, the reaction rate increases with the increase of temperature, and its law is similar to the law of an exponential function, that is, under fixed chlorine and carbon monoxide ratio conditions and at a certain temperature, the reaction rate is very slow, and the heat generated by the reaction in the process is absorbed by the reaction gas and the activated carbon (catalyst), thereby causing the temperature of the reaction gas and the catalyst to continue to rise; when the temperature is higher than a certain temperature, the reaction rate of phosgene synthesis will increase rapidly, and the heat generated by the reaction in the process is further absorbed by the reaction gas and the activated carbon (catalyst), causing the catalyst bed temperature to continue to rise until the reaction reaches equilibrium; the critical point of the catalyst bed temperature that triggers a rapid increase in the reaction rate of phosgene synthesis is approximately 120°C.

[0026] According to another study of the inventor of the present application on the phosgene synthesis process using activated carbon as a catalyst, it was found that the catalytic activity of activated carbon will decrease with the increase of reaction time, especially at the position with high reaction rate, such as the position near the inlet section of the tubular array containing catalyst at the initial operation of the phosgene synthesis device. After a period of operation, the catalytic activity of the catalyst at the inlet section of the catalyst bed decreases, the reaction progress of the catalyst bed section at a longer distance from the inlet of the tubular array containing catalyst decreases, the temperature of the reaction gas and the catalyst bed is low, and the outlet section of the tubular array containing catalyst will have an incomplete reaction of chlorine and carbon monoxide. At this time, it is necessary to reduce the ratio of chlorine to carbon monoxide, but this will lead to an increase in the carbon monoxide content in the gas phase at the reactor outlet.

[0027] Therefore, the present application controls the temperature of the catalyst bed within a suitable range by filling a variable temperature cooling medium on the side of the shell of the phosgene synthesis device, which can effectively reduce the light component content in the gas phase logistics at the outlet of the phosgene synthesis device, and then reduce the light component content in the liquid phosgene after condensation and separation, and can reduce the light component impurity content in the hydrogen chloride by-product logistics obtained in the isocyanate synthesis process, thereby achieving stable temperature control of the downstream hydrogen chloride catalytic oxidation reactor.

[0028] The cooling medium between the outer side of the tubular shell and the shell containing the catalyst can be selected from high-boiling point substances such as ethylene glycol, mineral oil, decalin (whose operating temperature is close to 120°C or higher), so that the inlet temperature of the catalyst bed in the tubular shell containing the catalyst is maintained at about 120°C or higher, thereby allowing the phosgene synthesis reaction to be carried out at a position close to the front section of the catalyst bed in the tubular shell containing the catalyst, which is conducive to improving the reaction conversion rate of the gas phase at the outlet of the photosynthetic reaction device, allowing the phosgene synthesis reaction to be carried out at a higher ratio of chlorine to carbon monoxide, and reducing the carbon monoxide content in the gas phase at the outlet of the reaction device. In addition, chlorine and the catalyst (activated carbon) will have side reactions in the phosgene synthesis process and produce light component substances, such as chlorinated alkanes and chlorinated olefins. When the reaction temperature is higher than 450°C, the reaction rate of the side reaction increases significantly, resulting in the generation of a large amount of chlorine-containing light component substances.

[0029] In some embodiments, the inlet temperature of the catalyst bed is maintained at 110-130° C. (e.g., 112° C., 114° C., 118° C., 120° C., 128° C.), preferably 115-125° C., by the cooling medium introduced into the phosgene synthesis reactor (for heat removal from the phosgene synthesizer), and the maximum temperature of the catalyst bed is maintained at 430° C. or less, preferably 360-430° C. (e.g., 365° C., 370° C., 380° C., 390° C., 400° C., 405° C., 410° C., 415° C., 420° C., 425° C.). Herein, the temperature distribution curve in the catalyst bed is peak-shaped, and the highest temperature point is reached in the middle of the catalyst bed.

[0030] In some embodiments, the phosgene synthesis device used in the above phosgene synthesis process can be a conventional device in the art, for example, it can include a plurality of parallel arranged tubes filled with catalysts, wherein activated carbon is filled as a catalyst, and the two sides of the catalyst tubes are welded into a tube sheet; a temperature detection device is installed in some catalyst tubes to monitor the temperature of the bed in the tubes filled with catalysts. The two ends of the tube sheet are designed with headers for sealing the material side, and the headers at both ends have pipe openings for feeding and discharging respectively.

[0031] In some embodiments, the temperature of the cooling medium between the outer side of the tubular shell containing the catalyst and the shell in the phosgene synthesis device is dynamically adjusted according to the indication of the temperature detection point in the tubular shell containing the catalyst, and the principle of dynamic adjustment is to maintain the catalyst bed inlet temperature close to 120°C, preferably 110-130°C, more preferably 115-125°C, while maintaining the maximum temperature of the catalyst bed below 450°C, preferably below 430°C, and more preferably below 400°C. When the requirements of the catalyst bed inlet temperature and the maximum bed temperature range cannot be met at the same time, the limited requirements of the catalyst bed maximum temperature are met first, because in the subsequent condensation separation process to obtain liquid-phase phosgene with a low content of light components, carbon monoxide is easier to separate than components such as chlorinated olefins and chlorinated alkanes, and the combustion heat of components such as chlorinated olefins and chlorinated alkanes is higher than that of carbon monoxide.

[0032] In some embodiments, the cooling medium is a high boiling point medium, preferably one or more selected from ethylene glycol, mineral oil and decalin.

[0033] In some embodiments, the purity of the carbon monoxide stream is 98.0% to 99.9% (eg, 98.5%, 99.2%, 99.5%), preferably 99.0 to 99.9%.

[0034] In some embodiments, the purity of the chlorine gas stream is 99.5% to 99.9% (eg, 99.6%, 99.8%), preferably 99.7% to 99.9%.

[0035] In some embodiments, the molar ratio of chlorine to carbon monoxide is 0.93-0.99 (eg, 0.94, 0.96, 0.98), preferably 0.95-0.99, and more preferably 0.97-0.99.

[0036] In some embodiments, the reaction pressure of the phosgene synthesis reaction is 3-7 barg (e.g., 3.5 barg, 4.5 barg, 5.0 barg, 5.5 barg, 6.5 barg), preferably 4-6 barg.

[0037] In some embodiments, the gas phase stream I discharged from the phosgene synthesis reactor is separated by a single stage condensation or a multi-stage condensation; the multi-stage condensation is preferably 2-5 (eg, 3, 4) stages of condensation.

[0038] In some embodiments, the temperature at the outlet of the condenser of the first-stage condensation separation is -30°C to -15°C (e.g., -28°C, -25°C, -20°C, -18°C); or, the temperature at the outlet of the last-stage condenser of the multi-stage condensation separation is -30°C to -15°C (e.g., -28°C, -25°C, -20°C, -18°C).

[0039] The condensation separation device and operation process are conventional choices in the art and will not be described in detail here. Through the condensation separation process, part of the light component impurities in the obtained crude phosgene stream can be removed.

[0040] In some embodiments, in the step of synthesizing the isocyanate, the isocyanate may be a diisocyanate, preferably selected from diphenylmethane diisocyanate and toluene diisocyanate.

[0041] In some embodiments, the isocyanate synthesis process is carried out in a liquid phase, and the solvent used in the liquid phase is selected from one or more of toluene, benzene, chlorobenzene and o-dichlorobenzene.

[0042] In some embodiments, the process conditions of the isocyanate synthesis step include: a reaction temperature of 70-150°C (e.g., 80°C, 100°C, 120°C, 140°C), and a reaction pressure of 0.2-0.6MPa (e.g., 0.25MPa, 0.3MPa, 0.4MPa, 0.5MPa).

[0043] Step (3) can obtain hydrogen chloride byproduct logistics through the synthesis process of isocyanate, and any synthesis process of isocyanate that can obtain hydrogen chloride logistics is applicable. Herein, the equipment and operation steps, reaction raw material types, material ratios, etc. used in the synthesis process of isocyanate can be achieved by conventional means in the art, and will not be repeated here. In addition, the selection of parameters such as reaction raw material types and material ratios can have a negligible effect on the types and contents of light component impurities in the hydrogen chloride logistics obtained by the synthesis process of isocyanate in step (3).

[0044] The hydrogen chloride stream with high purity (low light component impurity content) obtained by the method of the present invention can be used as a raw material in the process of producing chlorine by catalytic oxidation of hydrogen chloride.

[0045] In a specific embodiment, the process of producing chlorine by catalytic oxidation of hydrogen chloride can be implemented with reference to the record of patent document CN111167468 A. For example, it can be carried out in a fixed bed or fluidized bed reactor, or in other reactors suitable for such reactions. The oxidation reaction can be carried out in a fixed bed reactor. In a fixed bed reactor, after the catalyst is loaded, the reactor is replaced with air and / or oxygen and / or nitrogen as a medium, and then the temperature in the reactor is raised to 250-350°C, and the gas flow is gradually adjusted to hydrogen chloride and oxygen. Due to the exothermic reaction, the temperature of the catalyst bed will rise after hydrogen chloride and oxygen are introduced. The maximum temperature (hot spot temperature) in the reactor is controlled at 300-420°C, preferably 320-400°C, and more preferably 330-390°C.

[0046] In this article, "temperature fluctuation range" can be defined as the average variation range of the maximum temperature of the hydrogen chloride catalytic oxidation catalyst bed over a period of time (e.g., 12-24 hours or 2-5 days) when the raw material composition and other conditions remain unchanged. This indicator can be used to characterize the stability of the hydrogen chloride catalytic oxidation process.

[0047] The maximum temperature of the catalyst bed of the hydrogen chloride catalytic oxidation can be used to characterize the loss of catalyst life. When the maximum temperature of the catalyst bed exceeds the control value or the set value, it will lead to the loss of catalyst life.

[0048] By the method of the present invention, the temperature of the catalyst bed in the phosgene synthesis device is controlled within a suitable range, which can effectively reduce the light component content in the gas phase flow at the outlet of the phosgene synthesis device, and then reduce the light component content in the liquid phosgene after condensation separation, and can reduce the light component impurity content in the hydrogen chloride byproduct flow obtained in the isocyanate synthesis reaction, so as to achieve stable temperature control of the downstream hydrogen chloride catalytic oxidation reactor. For example, in the obtained liquid phosgene stream, the total mass content of light components is controlled at 5-2000ppm; in the hydrogen chloride flow, the total mass content of light components is controlled at 5-1500ppm; the obtained hydrogen chloride flow with low light component content is used for hydrogen chloride oxidation reaction, which effectively reduces the maximum temperature of the hydrogen chloride oxidation reactor (e.g., not exceeding 420°C) and reduces the temperature fluctuation range (e.g., not exceeding 1.1%). DETAILED DESCRIPTION

[0049] In order to understand the technical features and content of the present invention in detail, the preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described in the embodiments, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments described herein. For those who do not specify specific conditions in the embodiments, they are carried out according to normal conditions or the conditions recommended by the manufacturer.

[0050] <Source of raw materials>

[0051] In the following examples and comparative examples, the sources of some reagents or raw materials used are shown in Table 1. Other reagents or raw materials without manufacturer indicated are conventional products that can be purchased commercially.

[0052] Table 1

[0053]

[0054]

[0055] In the following examples and comparative examples, during the process of phosgene synthesis using the method of the present invention, the activated carbon bed layer used as the catalyst bed layer is the same.

[0056] In the following examples and comparative examples, the method for hydrogen chloride oxidation using the hydrogen chloride byproduct of the present invention as a raw material can be carried out by referring to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN 111167468A.

[0057] The present invention will be further described below with examples, but the present invention is not limited thereto.

[0058] Example 1

[0059] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 99.6%, the purity of the chlorine stream is 99.8%, and the molar ratio of chlorine to carbon monoxide is 0.95; and the pressure of the phosgene synthesis reaction is 5 bar;

[0060] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is ethylene glycol, and its temperature is 132°C. The inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 120°C, and the maximum temperature of the catalyst activated carbon bed is 396°C.

[0061] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -25°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0062] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis process as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize diphenylmethane diisocyanate; the reaction is carried out in the liquid phase, the solvent used is chlorobenzene, the reaction temperature is 140° C., and the reaction pressure is 0.4 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0063] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0064] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0065] Example 2

[0066] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 99.8%, the purity of the chlorine stream is 99.6%, and the molar ratio of chlorine to carbon monoxide is 0.93; and the pressure of the phosgene synthesis reaction is 4 bar;

[0067] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is mineral oil, and its temperature is 125°C; the inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 110°C, and the maximum temperature of the catalyst activated carbon bed is 385°C;

[0068] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -20°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0069] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis step as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize diphenylmethane diisocyanate; the reaction is carried out in the liquid phase, the solvent used is chlorobenzene, the reaction temperature is 100° C., and the reaction pressure is 0.2 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0070] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0071] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0072] Example 3

[0073] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene, wherein the purity of the carbon monoxide stream is 99.4%, the purity of the chlorine stream is 99.5%, and the molar ratio of chlorine to carbon monoxide is 0.98; the pressure of the phosgene synthesis reaction is 6 bar;

[0074] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is ethylene glycol, and its temperature is 153°C; the inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 130°C, and the maximum temperature of the catalyst activated carbon bed is 425°C;

[0075] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -15°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0076] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis process as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize diphenylmethane diisocyanate; the reaction is carried out in the liquid phase, the solvent used is chlorobenzene, the reaction temperature is 130° C., and the reaction pressure is 0.3 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0077] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0078] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0079] Example 4

[0080] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 98.5%, the purity of the chlorine stream is 99.9%, and the molar ratio of chlorine to carbon monoxide is 0.94; and the pressure of the phosgene synthesis reaction is 3 bar;

[0081] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is mineral oil, and its temperature is 132°C. The inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 115°C, and the maximum temperature of the catalyst activated carbon bed is 446°C.

[0082] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -30°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0083] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis process as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize toluene diisocyanate; the reaction is carried out in the liquid phase, the solvent used is o-dichlorobenzene, the reaction temperature is 120° C., and the reaction pressure is 0.5 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0084] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0085] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0086] Example 5

[0087] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 98.9%, the purity of the chlorine stream is 99.7%, and the molar ratio of chlorine to carbon monoxide is 0.97; and the pressure of the phosgene synthesis reaction is 7 bar;

[0088] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is decalin, and its temperature is 136°C. The inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 125°C, and the maximum temperature of the catalyst activated carbon bed is 407°C.

[0089] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation and cooled to a temperature of -25°C at the outlet of the condenser to separate and obtain a liquid phosgene stream containing light components;

[0090] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis process as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize toluene diisocyanate; the reaction is carried out in the liquid phase, the solvent used is o-dichlorobenzene, the reaction temperature is 125° C., and the reaction pressure is 0.6 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0091] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0092] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0093] Example 6

[0094] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 99.3%, the purity of the chlorine stream is 99.6%, and the molar ratio of chlorine to carbon monoxide is 0.96; the pressure of the phosgene synthesis reaction is 5 bar;

[0095] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is mineral oil, and its temperature is 157°C. The inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 123°C, and the maximum temperature of the catalyst activated carbon bed is 416°C.

[0096] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation and cooled to a temperature of -24°C at the outlet of the condenser to separate and obtain a liquid phosgene stream containing light components;

[0097] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis step as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize toluene diisocyanate; the reaction is carried out in the liquid phase, the solvent used is o-dichlorobenzene, the reaction temperature is 128° C., and the reaction pressure is 0.55 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream with a low light component content.

[0098] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0099] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0100] Comparative Example 1

[0101] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 99.4%, the purity of the chlorine stream is 99.6%, and the molar ratio of chlorine to carbon monoxide is 0.94; and the pressure of the phosgene synthesis reaction is 3 bar;

[0102] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is decalin, and its temperature is 235°C. The inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 126°C, and the maximum temperature of the catalyst activated carbon bed is 502°C.

[0103] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -30°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0104] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis step as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize diphenylmethane diisocyanate; the reaction is carried out in the liquid phase, the solvent used is chlorobenzene, the reaction temperature is 140° C., and the reaction pressure is 0.4 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream containing light components.

[0105] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0106] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0107] Comparative Example 2

[0108] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 98.3%, the purity of the chlorine stream is 99.8%, and the molar ratio of chlorine to carbon monoxide is 0.9; and the pressure of the phosgene synthesis reaction is 5 bar;

[0109] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is water, and its temperature is 50°C; the inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 50°C, and the maximum temperature of the catalyst activated carbon bed is 436°C;

[0110] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -25°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0111] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis step as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize diphenylmethane diisocyanate; the reaction is carried out in the liquid phase, the solvent used is chlorobenzene, the reaction temperature is 130° C., and the reaction pressure is 0.3 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream containing light components.

[0112] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0113] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0114] Comparative Example 3

[0115] (1) A carbon monoxide stream and a chlorine stream are introduced into a phosgene synthesis reactor, and a phosgene synthesis reaction is carried out under the catalysis of activated carbon to synthesize phosgene; wherein the purity of the carbon monoxide stream is 98.8%, the purity of the chlorine stream is 99.7%, and the molar ratio of chlorine to carbon monoxide is 0.91; and the pressure of the phosgene synthesis reaction is 4 bar;

[0116] The cooling medium used between the outer side of the tubes containing the catalyst and the shell in the phosgene synthesis reactor is water, and its temperature is 60°C; the inlet point temperature of the catalyst activated carbon bed is controlled by the cooling medium to be 55°C, and the maximum temperature of the catalyst activated carbon bed is 479°C;

[0117] (2) The gas phase stream I at the outlet of the phosgene synthesis reactor is subjected to primary condensation, and after being cooled to a temperature of -20°C at the outlet of the condenser, a liquid phosgene stream containing light components is separated;

[0118] (3) The liquid phosgene stream obtained above is fed into the isocyanate synthesis process as a reaction raw material, and a phosgenation synthesis reaction is carried out through conventional operations in the art to synthesize toluene diisocyanate; the reaction is carried out in the liquid phase, the solvent used is o-dichlorobenzene, the reaction temperature is 120° C., and the reaction pressure is 0.5 MPa; the gas phase stream II obtained by the reaction is condensed and impurities such as phosgene and solvent are removed to obtain a hydrogen chloride stream containing light components.

[0119] The light components contained in the liquid phosgene stream have the same composition as the light components contained in the hydrogen chloride stream, both of which are mixtures of chlorinated olefins, chlorinated alkanes and carbon monoxide.

[0120] The hydrogen chloride stream obtained as described above is applied to the process of producing chlorine by catalytic oxidation of hydrogen chloride (refer to the steps and process conditions for preparing chlorine by catalytic oxidation of hydrogen chloride disclosed in the catalyst performance test section in Example 1 of patent document CN111167468A), the reactor is a fixed bed reactor, and the maximum temperature of the catalyst bed is measured after the reaction stabilizes.

[0121] Table 2 Test results of various embodiments and comparative examples and temperature of hydrogen chloride oxidation reactor

[0122]

[0123]

[0124] It can be seen from the experimental results in Table 2 that, in each embodiment, the cooling medium between the outer side of the tubular shell equipped with the catalyst and the shell is temperature-controlled and combined with the reaction process conditions of phosgene synthesis (e.g., reaction pressure, molar ratio of chlorine to carbon monoxide, etc.), the inlet temperature and the maximum temperature of the phosgene synthesis catalyst bed can be controlled within a suitable range, the content of light components such as carbon monoxide, chloroolefins and chloroalkanes in the obtained liquid phosgene can be reduced, and the content of light components in the hydrogen chloride stream obtained in the isocyanate production process can be reduced; the use of the obtained hydrogen chloride byproduct with low light component content for hydrogen chloride oxidation reaction can effectively reduce the maximum temperature of the hydrogen chloride oxidation reactor (no more than 420°C) and reduce the temperature fluctuation range (no more than 1.1%). In each comparative example, the inlet temperature and the maximum temperature of the phosgene synthesis catalyst bed are not controlled within a suitable range, and the content of light components in the liquid phosgene and hydrogen chloride byproduct streams is high, which is not conducive to the stable operation of the hydrogen chloride oxidation reactor.

[0125] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for obtaining hydrogen chloride with low light component content in an isocyanate production process, characterized in that: The steps include: (1) A chlorine gas stream and a carbon monoxide stream are introduced into a phosgene synthesis reactor to carry out a phosgene synthesis reaction under the catalysis of a catalyst to synthesize phosgene; wherein the inlet temperature of the catalyst bed of the phosgene synthesis reactor is controlled at 110° C. or above, and the maximum temperature of the catalyst bed is controlled at 450° C. or below; (2) condensing and separating the gas phase stream I discharged from the phosgene synthesis reactor to obtain a liquid phosgene stream with a low content of light component i; (3) The obtained liquid phosgene stream is fed into the isocyanate synthesis step as a reaction raw material to carry out a phosgenation synthesis reaction. The gas phase stream II produced by the reaction is condensed and impurities are removed to obtain a hydrogen chloride stream with a low light component II content.

2. The method according to claim 1, characterized in that The liquid phosgene stream contains light components i, and the composition of the light components includes: one or more of chlorinated olefins, chlorinated alkanes and carbon monoxide.

3. The method according to claim 1 or 2, characterized in that: In the liquid phosgene stream, the total content (mass ratio) of the light component i is controlled at 5-2000 ppm, preferably 10-1000 ppm, and more preferably 20-300 ppm.

4. The method according to any one of claims 1 to 3, characterized in that In the hydrogen chloride stream, the light component ii comprises one or more of chlorinated olefins, chlorinated alkanes and carbon monoxide; In the hydrogen chloride stream, the total content (mass ratio) of the light component ii is controlled at 5-1500 ppm, preferably at 10-750 ppm, and more preferably at 20-250 ppm.

5. The method according to any one of claims 1 to 4, characterized in that The compositions of the light component i and the light component ii are the same or different, preferably the same.

6. The method according to any one of claims 1 to 5, characterized in that The cooling medium introduced into the phosgene synthesis reactor is used to maintain the inlet temperature of the catalyst bed at 110-130°C, preferably 115-125°C, and the maximum temperature of the catalyst bed is maintained at 430°C or below, preferably 360-430°C.

7. The method according to any one of claims 1 to 6, characterized in that The cooling medium is a high boiling point medium, preferably one or more selected from ethylene glycol, mineral oil and decalin.

8. The method according to any one of claims 1 to 7, characterized in that The purity of the carbon monoxide stream is 98.0% to 99.9%, preferably 99.0% to 99.9%; and / or The purity of the chlorine gas stream is 99.5% to 99.9%, preferably 99.7% to 99.9%; and / or The molar ratio of chlorine to carbon monoxide is 0.93-0.99, preferably 0.95-0.99, more preferably 0.97-0.

99.

9. The method according to any one of claims 1 to 8, characterized in that The reaction pressure of the phosgene synthesis reaction is 3-7 barg, preferably 4-6 barg; and / or The gas phase stream I discharged from the phosgene synthesis reactor is separated by a single condensation or a multi-stage condensation; the multi-stage condensation is preferably separated by 2-5 stages; The temperature at the outlet of the condenser of the first-stage condensation separation is -30°C to -15°C; or, the temperature at the outlet of the last-stage condenser of the multi-stage condensation separation is -30°C to -15°C.

10. The method according to any one of claims 1 to 9, characterized in that In the isocyanate synthesis step, the isocyanate is a diisocyanate, preferably selected from diphenylmethane diisocyanate and toluene diisocyanate; and / or The isocyanate synthesis process is carried out in a liquid phase, and the solvent used in the liquid phase is selected from one or more of toluene, benzene, chlorobenzene and o-dichlorobenzene; and / or The process conditions of the isocyanate synthesis step include: a reaction temperature of 70-150° C. and a reaction pressure of 0.2-0.6 MPa.

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